Any discussion of the prior art throughout the specification is not an admission that such prior art is widely known or forms part of the common general knowledge in the field.
It is known to produce composite products from waste products containing cellulosic materials by chemically transforming the natural sugars into a bonding and bulking agent by the application of heat and pressure. Such methods have been used for many years and one well-known method is generally called ‘explosion hydrolysis’. That method consists in placing the material to be processed in a strong closed vessel, passing high-pressure steam into the vessel for a specific period and then opening the vessel in such a manner that the material explodes out of the vessel. In particular the explosion process affects hemicellulose, which is a non-structural component of woody material. During the explosion process hemicellulose is broken down initially into simpler sugars, which are further transformed with other products during the explosion process to form the resinous material that bonds the product.
U.S. Pat. No. 1,578,609 granted in 1926 to William H Mason of USA described a process and apparatus for the disintegration of lignocellulosic material. The method consisted in the chipping of small pieces of timber, placing them in a closed high pressure chamber, commonly known as a ‘gun’ and subjecting the material to pressure by steam, compressed air or the like. After sufficient time to allow the gases to penetrate the wood and to establish a balance of pressure and temperature in the wood, an outlet valve of comparatively small dimension is opened to cause the material to be forcibly driven out of the chamber through the valve opening. As the pieces of wood emerge, they are progressively disintegrated.
This method, described in U.S. Pat. No. 1,578,609, has subsequently become known as ‘explosion hydrolysis’ and further discussion on this method can be found in the specification of U.S. Pat. No. 2,303,345 (Mason and Boehm), which describes a process for making products from lignocellulosic material by using high pressure steam in a gun to separate the lignin from ligno-cellulose and to hydrolyse the hemicellulose into water-soluble material.
The disadvantage with the process disclosed in the U.S. Pat. No. 2,303,345, known as the ‘Masonite’ process, is that it produces a water-soluble adhesive so that the adhesive bond formed by the Masonite process tends to liquefy with a consequent deterioration of the quality of the product.
U.S. Pat. No. 5,017,319 (Shen), discloses a process for converting hemi-cellulosic materials into a thermoset waterproof adhesive. The process consists in bringing lignocellulosic material which contains at least 10% hemicellulose into contact with high pressure steam to decompose and hydrolyse the hemicellulose into a resin material without significant carbonisation of the hemicellulose. The material is then heated and pressed against a surface to thermoset and adhere the material to the surface.
U.S. Pat. No. 5,328,562 (Rafferty and Scott), describes a process and an apparatus for producing a lignocellulosic product whereby the lignocellulosic material is hydrolysed in a primary zone and the product is moved from the primary zone to a secondary zone into which superheated steam bled from the primary zone is introduced under sufficient pressure to dry the hydrolysis products. This specification is concerned with a continuous energy re-circulation system so there will be a minimum of waste energy in the process.
It is also well known that the quality of a product formed by the explosion process depends largely on how well the adhesive polymer produced during the explosion process is spread throughout the material and how well the material is compacted. The temperature during the process is very important because if the temperature is too high, degradation of the natural sugars would occur and this would produce water and reduce the efficiency of the surface coating and of the adhesive resulting in a weaker and less water-repellent product. If the temperature is too low, a less efficient dispersal of the adhesive polymer occurs and that would result in a product that might not have the desired qualities. Therefore the water content management of the process is vital for good process performance.
In addition, it is known that both furan and hydroxymethylfuran, which are sugars from which water has been removed, are often present in the processed product. This can occur at high temperatures where there is little free water and where reactions occur which demand water, such as when lignin is being broken down. Furans are reactive and will readily take part in the lignin repolymerisation process and even small amounts will assist to link together large molecules in the processed product. Consequently it is necessary to control the amount of moisture very closely to produce a satisfactory product.
In U.S. Pat. No. 7,303,707 (Rafferty '707) the hydrothermal processing of lignocellulosic materials with between 11% and 25% moisture by hydrothermal processing is discussed. The inventors indicate that around 16% moisture content in the feedstock is optimum. Materials with an initial moisture content outside 11% to 25% are not felt suitable for processing, and in fact the document does not mention processing of materials outside this range. Rafferty '707 indicates that the initial moisture content is an important consideration and uses dry saturated or slightly (up to 5° C.) superheated steam to process the lignocellulosic material. There are many natural materials containing lignin, hemicellulose or cellulose, alone or in combination, that fall outside of the 11% to 25% range proposed. For example large quantities of Distillers Dry Grain (DDG), Distillers Dry Grain and Solubles (DDGS) and spent corn used for ethanol production are dried to below 11% for storage, thus fall outside this 11% to 25% moisture content range. Given Rafferty '707 indicates that the moisture content should be between 11% and 25%, preferably 16% it apparently discounts processing materials outside this range. Given the control of moisture content is critical to the process the moisture content of the raw material is carefully controlled. The use of dry saturated steam (with up to 5° C. superheat) is indicated in Rafferty '707, this again confirms that careful control of the moisture content of the raw material and water present for the reactions inside the hydrothermal pressure vessel are carefully controlled. They reinforce the message that careful control of moisture content is critical to producing a useful product.
US Published Patent Application Number 2009/0110654 is directed to providing a low odour biocomposite by processing lignocellulosic material by the method described in U.S. Pat. No. 7,303,707. US 2009/0110654 does not introduce any method of hydrothermally processing lignocellulosic material outside of that disclosed in U.S. Pat. No. 7,303,707. For example, US 2009/0110654 specifically discloses the process described in U.S. Pat. No. 7,303,707 in paragraph 0010, referring to it by its application Ser. No. 10/494,646 and calling it the Lignotech method:                “U.S. patent application Ser. No. 10/494,646, published on Aug. 11, 2005, teaches a method of processing ligno-cellulosic material using hydrothermal pressure vessel, the entire disclosure of which is incorporated by reference. This method includes steps of comminuting of the material, drying, subjecting the material packed vessel to steam under pressure, and then drying the processed material to a specific moisture content. This method is referred to as LignoTech and may be utilized as one method of preparing a biological material to be integrated with a plastic material and an odor controlling agent in some embodiments of the present invention.”        
When the ‘Lignotech process’ is discussed later in US 2009/0110654 (paragraph 0072) the exact range of moisture content taught by U.S. Pat. No. 7,303,707 is specified:                “When the biological material is dried in moving air, the air velocity is regulated along with the temperature of the air to ensure adequate drying of the material, preferably to a moisture content between 11% to 25%, although a higher moisture content may also work for some applications. The best results have been obtained with the dried material with around 16% moisture content.”        
At no point in US 2009/011654 is any method other than the ‘Lignotech process’ discussed, and it teaches very careful control of moisture content for the process. There is no positive disclosure in US 2009/011654 or U.S. Pat. No. 7,303,707 of a process using a feedstock moisture content below 11%, thus any references to below 25% moisture content teach only 11% to 25% moisture content in the feedstock.
US 2009/011654 is directed to a de-odorising solution for bio-plastic composite materials, a combination of polymers and filler materials such as DDG, when hydrolysing is mentioned in the examples, see paragraph 0107, it specifically states:                “Next, the biological material particulate is dried appropriately for a hydrolysis process.”        
The only hydrolysis process mentioned or discussed is that described in U.S. Pat. No. 7,303,707, which specifies a moisture content of between 11% and 25%. Processing outside of this moisture content range is taught away from.
One further disadvantage with many of the hydrothermal explosive decompression processes described above is the stress applied to the valve used to decompress and eject the material processed. With processes decompressing from 30 bar, or higher, to atmospheric, in 2 seconds or less, the valves used either have a short life or are very expensive (often both).
It is an object of the present invention to provide a means of processing lignocellulosic materials.